Circadian organization means the way in which the entire circadian system above the cellular level is put together physically and the principles and rules that determine the interactions among its component parts which produce overt rhythms of physiology and behavior. Understanding this organization and its evolution is of practical importance as well as of basic interest. The first major problem that we face is the difficulty of making sense of the apparently great diversity that we observe in circadian organization of diverse vertebrates. Some of this diversity falls neatly into place along phylogenetic lines leading to firm generalizations: i) in all vertebrates there is a "circadian axis" consisting of the retinas, the pineal gland and the suprachiasmatic nucleus (SCN), ii) in many non-mammalian vertebrates of all classes (but not in any mammals) the pineal gland is both a photoreceptor and a circadian oscillator, and iii) in all non-mammalian vertebrates (but not in any mammals) there are extraretinal (and extrapineal) circadian photoreceptors. An interesting explanation of some of these facts, especially the differences between mammals and other vertebrates, can be constructed on the assumption that early in their evolution mammals passed through a "nocturnal bottleneck". On the other hand, a good deal of the diversity among the circadian systems of vertebrates does not fall neatly into place along phylogenetic lines. In the present review we will consider how we might better understand such "phylogenetically incoherent" diversity and what sorts of new information may help to further our understanding of the evolution of circadian organization in vertebrates. Key wordsOrganisms, from unicellulars to vertebrates, are structured in time as well as in space. Many, if not most, biochemical, physiological and behavioral parameters exhibited by organisms show daily fluctuations and most of these daily rhythms persist in constant conditions, thus demonstrating that they are driven by endogenous oscillators. The rhythms that persist in constant conditions with periods close to 24 h are called circadian rhythms.By circadian organization we mean the way in which the entire circadian system above the cellular level is put together physically, and the principles and rules that determine the interactions among its component parts. Circadian organization extends both broadly and deeply into the physiology and

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Previous application of a Portuguese version of the Horne and Östberg (H&O) questionnaires in Brazil showed a displacement of the distribution of Morningness/Eveningness (M/E) types towards morningness, demanding a reclassification of the score's limits for each of the 5 possible M/E types. Among city, age and sex, city was the only factor determining significant group differences. In the present paper, the same version of the H&O's questionnaire was applied to a distinct population of 260 adults, balanced according to age, sex and city. Data were collected from October to December, to control the effect of the photoperiod. City remains the only factor determining significant group differences (p<0.001). Moreover, there does not appear a coherent latitude trend that could explain differences among cities as a function of photoperiod. Local social habits could probably explain our results, suggesting further investigations of peculiar temporal patterns.

Daily locomotor activity in common marmosets shows a decrease near the middle of the active phase, as observed for captive and wild living animals. An important 8 h period component detected in spectral analysis shows annual variation. To determine the environmental factors that are correlated with this finding, three animals were observed during infant and juvenile stages in outdoor cages under natural temperature, humidity and light cycles. Data were collected from sunrise to sunset, three consecutive days a week, at 5 min intervals randomly distributed inside the clock hours, and were recorded as the total of arbitrary cage sections traveled by the animal each interval. From the Fourier analysis of weekly data series we calculated the relative power of the 8 h period component. Pearson's correlation test showed that the relative power correlates better with environmental temperature and photophase duration than with relative humidity or rainfall. Amplitude but not acrophase showed significant differences (Kruskall-Wallis test, p<0.01) between seasons. These findings suggest that the annual variation in the 8 h period component could result from a temperature modulation on the locomotor activity rhythm.

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One family group of common marmosets (Callithrix jacchus) maintained in captivity under natural environmental conditions (Natal, Brazil, 05°46¢S, 35°12¢W) was observed by focal sampling at two non-consecutive days per week during two nonconsecutive pregnancies (pregnancy 1: the last 8 fortnights before parturition; pregnancy 2: the last 5 ones) and after parturition (4 fortnights for both). The hourly percentiles of the duration of self-grooming and allogrooming interactions of the reproductive pair were submitted to Cosinor analysis for the 24-h period (p £ 0.05). The reproductive female's progesterone was monitored by fecal collection twice a week between 7:00 h to 9:00 h. Levels of progesterone were determined by ELISA method. During pregnancy 1, all interactions of the reproductive pair showed a 24-h statistically significant period. However, after parturition this periodicity is not present in some behaviors of the reproductive male. This animal presents the 24-h periodicity only toward to the reproductive female, the subadult son and to the newborns. Hormonal levels of the reproductive female showed isolated increases above 100 ng/g at the second and third fortnight after parturition, but did not characterize ovulation. Between pregnancy 1 and 2, the family was increased by the birth of four animals.During pregnancy 2, a statistically significant 24-h period was find only in selfgrooming of the reproductive male and female, and in the interactions between the reproductive pair. Also, in the interactions of the reproductive male with only one of the juvenile son. After parturition the reproductive female ovulated at the second fortnight and became pregnant again. At this time, those interactions still have a 24-h period, except in grooming directed to the juvenile son by the reproductive male. As in the first post-partum, grooming directed to the newborns showed statistically significant 24-h period. These results suggest that the reproductive pair performs 24-h rhythmic grooming interactions only with some animals, supposed to be the preferential grooming partners. Furthermore, the temporal grooming expression in common marmosets may be affected by the reproductive condition (progesterone levels) of the reproductive female, by the care of newborn after parturition and the group size.

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